X-ray detectors used, for example, for examining objects or patients by way of an imaging method are intended to have the highest possible dynamic range or contrast range relative to the radiation power or the X-ray dose, since the relevant information is obtained precisely by the detection of local intensity differences in the X-ray radiation impinging on an X-ray detector and is thus detected as contrast differences.
In this case, on the one hand, it is often necessary to detect very large intensity differences, that is to say for example intensity differences between X-ray radiation which propagates past the object to be examined or past the patient to be examined in the direction of the X-ray detector and X-ray radiation which transmits through the object to be examined or the patient to be examined, and, on the other hand, very fine intensity differences are intended to be detected in order, on the basis of these intensity differences, to be able to differentiate between different materials within the volume of the object to be examined or between different types of tissue in the body of the patient to be examined.
However, the dynamic range of present-day X-ray detectors typically does not suffice to image the entire desired dynamic range, that is to say the desired contrast value range with the desired contrast resolution. Modern digital X-ray detectors instead generally have an adjustable sensitivity setting by means of which an operator can adapt the available dynamic range of the detector to the respective situation, such that at least the most important dynamic range for an examination is detected during an examination of an object or patient. If a greater dynamic range is nevertheless intended to be detected, a plurality of recordings of the object or patient with different settings for the exposure are made successively in order in this way to detect a subrange of the dynamic range with each recording.
Since, in most cases, the factor limiting the dynamic range is not to be found in the X-ray-sensitive sensor elements themselves, but rather in the downstream read-out electronic system, there are various approaches for subsequently conditioning the measurement signals of the X-ray-sensitive sensor elements in order in this way to extend the dynamic range or at least expediently predefine the available range of values.